1. Field of the Invention
This invention is related in general to the field of solar telescopes. In particular, it relates to a targeting system integrated within the body of a solar telescope.
2. Description of the Related Art
Solar telescopic observation requires that the objective of the telescope be precisely aligned with the sun. Because the angular size of the sun, viewed from the earth, is about 0.5°, pointing a solar telescope with a commensurate field of view precisely towards the sun is not an easy task. This difficulty is further exacerbated by the fact that the user of the telescope cannot look directly at the sun without harming his or her eyes.
Rough alignment of solar telescopes is typically achieved merely by pointing the telescope aperture in the general direction of the sun and minimizing the shade cast by the telescope. Since most telescopes have a tubular configuration, this process is rather simple to carry out. However, this type of alignment is often not sufficiently precise because of the small angles subtended by the sun. More sensitive aids for aligning solar telescopes with the sun consist of stand-alone units attached to the outer surface of the tube of the telescope. These aids operate in a fashion similar to the aiming scopes on rifles, with a small aperture projected in direct sunlight onto a viewing screen (both located in a unit mounted on the telescope's tube). When the projected sunspot is aligned with the center of the screen, the telescope is aimed at the sun. A similar pointing system is described in U.S. Patent Publication No. 2004/0027660, which includes a gnomon attached to the exterior of the telescope frame to project a shade in direct sunlight onto a viewing surface. When the telescope is aligned with the sun, the shade is eliminated, thereby enabling the targeting of the telescope towards the sun.
Thus, all currently available telescopes are either devoid or an aiming mechanism or are equipped with an external unit attached to the body of the telescope. The latter types are tubular units disposed in parallel to the tube of the telescope, so that the respective optical axes point to the same target at infinity. This configuration suffers from several problems that over time tend to affect the performance of the aiming mechanism. First, from a mechanical point of view, the exterior attachment of the aiming unit to the housing of the telescope subjects it to unavoidable bumps and other stressing forces applied by users that cause misalignment of the unit's optical axis with respect to that of the telescope. Second, from an optical point of view, these units transmit an unfolded image, which require observation in the direction of the sun during the alignment process. This is often unfortunate because the sun's brightness makes it difficult to identify and follow the image formed on the aiming unit's viewing screen. Moreover, the telescope's imaging system is often folded toward an eyepiece placed off-axis with respect to the optical axis of the objective, which implies that a user of the telescope has to switch position to use the aiming unit and the eyepiece.
Therefore, there is still a need for a telescope aiming device that overcomes the problems of prior-art units. This invention achieves these goals by integrating the targeting system and the viewing screen within the body of the solar telescope.